1. Field of the Invention
This invention relates generally to a video tape recorder (VTR) having a built-in camera and more particularly is directed to a power control circuit for a color encoder of a video camera for generating a video signal of the standard system.
2. Description of the Prior Art
In a video tape recorder having a built-in camera in which a luminance signal and a chrominance signal are respectively recorded on separate channels simultaneously, there is frequently employed such a recording system as shown in FIGS. 1A and 1B.
According to the recording system shown in FIGS. 1A and 1B, of a luminance signal and a chrominance signal derived from a television camera, a chrominance signal, for example, a pair of color difference signals R-Y and B-Y are respectively time-base-compressed to 1/2 of the normal ones. Also, a time division compressed color difference signal C, which results from time-dividing and frequency-multiplexing the pair of these color difference signals R-Y and B-Y as shown in FIG. 1B, and a luminance signal Y are simultaneously recorded on adjacent tracks as shown in FIG. 2.
In FIGS. 1A and 1B, reference letter P.sub.H designates a horizontal synchronizing pulse and reference letters P.sub.Y and P.sub.C designate reference pulses used for adjusting the time base, respectively.
FIG. 3 schematically shows one example of a circuit arrangement of the prior art video tape recorder having a built-in camera which employs such recording system.
In FIG. 3, reference letter 10 generally designates a built-in camera type VTR which comprises a televsion or video camera section 10A and a VTR (built-in type VTR) 10B. The VTR 10B is freely detachable from the video camera section 10A. An object is projected through a lens L to an image pickup device (image pickup tube or image pickup element using semiconductors, such as, CCDs (charge coupled devices) and the like). In this case, the object is projected onto the image pickup tube 1 for convenience sake of explanation. The image pickup signal from the image pickup tube 1 is supplied to a signal processing circuit 2 which forms, for example, a luminance signal Y and a pair of color difference signals R-Y and B-Y.
The luminance signal Y and the pair of color difference signals R-Y and B-Y are delivered to output terminals 3A, 3B and 3C, respectively. To these output terminals 3A, 3B and 3C, there is detachably coupled the built-in camera type VTR 10B. Accordingly, when the VTR 10B is connected to the output terminals 3A, 3B and 3C, the color difference signals R-Y and B-Y with the time-base-compressed as shown in FIG. 1B together with the luminance signal Y are simultaneously recorded on the two channels.
Referring to FIG. 3, a synchronizing signal generator 5 is adapted to generate a synchronizing signal SYNC. This synchronizing signal SYNC is supplied to an adder 6 in which it is superimposed upon the luminance signal Y.
The luminance signal Y with the synchronizing signal SYNC superimposed thereon and the pair of color difference signals R-Y and B-Y are further supplied to a color encoder 7 which generates a standard video signal (composite television signal) SC. This video signal SC is supplied through an amplifier 8 and a matching resistor 9D (its resistance value is 75.OMEGA.) to an external output terminal 3D. In this illustrated example, in parallel to the resistor 9D, there is connected another resistor 9E from which an external output terminal 3E is led out. Thus, the two-channel arrangement is formed.
Since the standard video signal SC is developed at these external output terminals 3D and 3E, if a standard VTR (not shown) is coupled thereto, it becomes possible to record the standard video signal SC. Alternatively, if a monitor television receiver is coupled thereto, it becomes possible to monitor an image picked-up output.
By the way, in the video tape recorder having a built-in camera 10 arranged as described above, the built-in type VTR 10B and the standard VTR can be used selectively. Accordingly, even when the built-in type VTR 10B is used, while the standard VTR is not used, the operation power is incessantly supplied to the color encoder 7 provided within the video camera section 10A.
In such use, it is not necessary to supply the power to the color encoder 7. However, in the prior art VTR having a built-in camera, the color encoder 7 is incessantly powered and so, there arises a problem that the power consumption becomes large. Particularly, the power that the color encoder 7 consumes amounts to about 1/2 of the whole power consumption. Therefore, how to reduce the power is a significant technical problem of the built-in camera type VTR that should be solved.